Choosing the Right Halftone Dot Shape

As you can see in fig. 11.12, the quality of the result when using Unsharp Mask depends very much on a low Radius setting and whether the color within the image is included in the adjustment or left out.

Round dots are fine for almost every application, but there might be occasions when an oval, or perhaps a diamond dot, will produce a better print. The reason for this is because of what happens when two dots meet.

As dot size increases, the point at which they touch gets closer and closer. As this happens, the percentage of the tint increases. When they actually touch, they grab onto each other as if they were long-parted friends. This creates a tint jump, and several percentage points of tint value are lost as a result (fig. 11.13).

If you are printing an image in which the middle-range color values are particularly important—Caucasian flesh tones, for example—and you want to get as much out of the tint range as you possibly can, an oval dot would be a better choice than a round dot.

This is because the single tint jump that happens when using a round dot is divided into two smaller tint jumps when you use an oval dot. Round dots suddenly join up on four sides, but oval dots first collide at each end and then, farther toward the shadows, they overlap at the top and bottom as well (fig. 11.14).

The result is a small tint jump slightly to the highlight side of the mid-tones, and another small tint jump out toward the shadows. The area between these is where most of the flesh tones will print.

Diamond dots are actually square, but if we were using just one color—black—we would set the screen at an angle of 45°, therefore all the squares would be tipped onto one corner (fig. 11.15)—hence “diamond.”

This shape allows completely even tone reproduction right up to around 90% density; then suddenly everything fills in completely. The dots join up not at single points but along whole sides. So, it is a very good shape to use for images that do not have any dense shadow areas.

	Usually the dot shape is a feature of imagesetter printing rather than something to deal with yourself, so it is important to tell the printer where you want it applied.